Applicants claim priority under 35 U.S.C. §119 of German Application Nos. 103 08 249.2 and 10 2004 009 066.1 filed Feb. 25, 2003 and Feb. 23, 2004, respectively.
1. Field of the Invention
The present invention relates to a device for the generation of tunable light pulses, having a non-linear optical fiber, by means of which the optical spectrum of femtosecond light pulses can be modified, taking advantage of solitonic effects.
2. The Prior Art
Laser systems that are able to produce femtosecond light pulses are increasingly being used in basic physical research and also in other areas of research. Using such laser systems, it is possible to observe rapid physical, chemical, and biological processes essentially in “real time.” Commercial areas of use for laser systems that produce femtosecond light pulses exist in the fields of materials examination and processing, in the field of medicine, as well as in the so-called “life science” field. Concrete applications that can be mentioned as examples are multi-photon microscopy as well as optical coherence tomography.
Particularly in the field of single-photon and multi-photon microscopy, there is a need for laser systems that are both high-performance and spectrally variable, which are inexpensive and easy to operate. Until now, femtosecond light pulses having a high performance in the laboratory were usually generated by means of titanium-sapphire laser systems. It is a disadvantage of these systems that they are very expensive, complicated to adjust, and difficult to handle. Also, the spectral tunability of the generated light pulses is not satisfactory in such laser systems.
Nowadays, there is a tendency towards generating femtosecond light pulses with pulse energies of one nanojoule and more by means of purely fiber-based laser systems. Such systems usually consist of a pulsed laser light source, which emits femtosecond light pulses in the energy range of 100 picojoules. These light pulses are then amplified, by means of an optically pumped amplifier fiber, so that the light pulses are available in the desired pulse energy range.
For example, a device for generating tunable light pulses is previously known from EP 1 118 904 A1. This device works with a special non-linear optical fiber. By means of this fiber, the optical spectrum of femtosecond light pulses that are provided by a suitable pulsed laser light source can be modified, in targeted manner, taking advantage of solitonic effects. To vary the spectrum of the generated light pulses, the intensity of the light coupled into the non-linear optical fiber is varied in the system described in the cited reference. This approach directly results in the disadvantage that in the previously known system, the desired optical spectrum of the generated light pulses is dependent on the pulse energy. An independent variation of the pulse energy and the wavelength of the light pulses is therefore not possible, using the previously known system. Another disadvantage is that in the previously known system, the non-linear fiber used must have a length of several 10 m, so that the desired solitonic optical effects become active to a sufficient degree. Because of the long traveling distance, an undesirable loss of coherence of the generated light pulses can occur.